1. Field of the Invention
This invention relates to novel concentrates of a highly branched polymer and functional fluids, e.g., lubricating oils, prepared from such concentrates. The polymer acts as a viscosity index improver and thickener for the functional fluid.
2. Information Disclosure Statement Including Description of Related Art
The following information is being disclosed under the provisions of 37 CFR 1.56, 1.97 and 1.98.
Functional fluids such as lubricating oils often contain a dissolved polymer for the purpose of improving their viscosity index (VI) and/or thickness. In general, various types of straight chain homopolymers and random and graft copolymers used as functional fluid additives may be prepared by anionic or free radical polymerization, while star-branched copolymers are usually prepared by anionic polymerization. In many instances of polymers prepared from hydrocarbon monomers, the polymer is separated by coagulating from an emulsion polymerization medium or precipitating from a solution polymerization medium and, after subjecting the polymer to any of various purification steps, mixing the solid polymer with a small amount of a base stock oil to form a concentrate. In other instances, the concentrate is formed by carrying out the polymerization in a volatile organic solvent such as hexane, adding oil to the resulting polymer solution, and evaporating the volatile solvent. In either case, the final functional fluid is formed by mixing the concentrate with an additional amount of base stock oil, which may be the same or different from the base stock oil in which the polymer is dissolved to form the concentrate.
The mixing of a polymer concentrate rather than solid polymer with the final amount of base stock oil to form the functional fluid facilitates mixing and results in a more homogeneous functional fluid. However, the mixing of solid polymer with the initial base stock oil to form the concentrate may be a difficult and expensive procedure, particularly when the polymer is highly branched and may not produce a concentrate or final functional fluid having the desired degree of homogeneity. On the other hand, the process of preparing the concentrate by carrying out the polymerization in a volatile organic solvent, adding base stock oil, and evaporating the solvent, includes the necessity of handling the solvent consistent with environmental requirements, and using equipment and energy to evaporate and recover the solvent, which could also involve substantial expense. Thus, any process of preparing a polymer concentrate and a functional fluid containing a highly branched polymer additive which raises substantially the viscosity index and thickness of the functional fluid, while avoiding the necessity of dissolving the solid polymer in a base stock oil, or of adding the oil to a solution of the polymer in a volatile organic solvent which must then be evaporated, is very desirable.
The following prior art references show aspects of the use of polymers as viscosity index improvers in functional fluids, and the preparation of branched polymers from monofunctional monomers such as styrene and multifunctional cross-linking agents such as divinylbenzene.
U.S. Pat. No. 3,318813, issued May 9, 1967 to McCormick et al., discloses polymers of alkylstyrenes, e.g., tert-butylstyrene, as additives for improving the viscosity index of lubricating oils. There is no suggestion in this patent of the production or use of any highly branched polymers.
U.S. Pat. No. 3,752,794, issued Aug. 14, 1973 to Bacakal, discloses copolymers of p-tert-butylstyrene with a nitrogen-containing comonomer prepared by free-radical polymerization, used as viscosity index improving dispersants in lubricating oils. There is no suggestion in this patent of any highly branched polymers.
U.S. Pat. No. 3,985,830, issued Oct. 12, 1976 to Fetters, teaches star-branched polymers produced by anionic polymerization and containing at least three arms of a copolymer of butadiene and styrene or isoprene and styrene, or a homopolymer of butadiene, isoprene, styrene radiating from a nucleus composed of at least two molecules of a linking compound such as divinylbenzene (DVB). There is no suggestion in this patent of the preparation of a highly branched polymer having segments of a polymer of p-tert-butylstyrene (t-BS) by free radical polymerization, in situ polymerization in a base stock oil, or use of the polymer as a viscosity index improver.
U.S. Pat. No. 4,611,031, issued Sep. 9, 1986 to Gallucio et al., discloses the preparation of compatibilizers for blends of an olefin copolymer and a polymethacrylate polymer, useful as lubricating oil additives, by a free-radical initiated graft polymerization of alkyl methacrylate monomers onto a separately prepared olefin copolymer in a base stock oil as solvent. Additional quantities of olefin copolymer, polymethacrylate polymer, and base oil stock may be added to the compatilizer solution to obtain a finished lubricating oil. There is no suggestion in this patent of the in situ preparation of any solution in a base stock oil of a highly branched polymer containing segments of a polymer of p-tert-butylstyrene, for use as a lubricating oil or other functional fluid.